Centrifuges



March 1967 e. TROJAN 3,307,703

CENTRIFUGES Filed Feb. 10, 1966 I 2 Sheets-Sheet 1 March 7, 1967 (5. TROJAN 3,307,703

- CENTRIFUGES 4 Filed Feb. 10, 1966 I 2 S eets-She 2 WWA N Fig.3

United States Patent Ofiice 3,397,703 Patented Mar. 7, 1967 3,307,703 CENTRHFUGES Giinter Trojan, Bochum-Harpen, Germany, assignor to Hein, Lehmann & Co. Airtiengesellschaft, Dusseldorf, Germany Filed Feb. 10, 1966, Ser. No. 526,477

Claims priority, application Germany, Mar. 27, 1965,

7 Claims. (Cl. 21036) This invention relates to centrifuges for continuously separating mixtures of solids and liquids, especially viscous sugar compositions, the centrifuge being of the kind comprising a perforated centrifuging and screening drum which rotates about a vertical axis, and two annular chambers which are disposed concentrically around the drum and are separated from one another by an annular partition extending to the top edge of the drum, one of the annular chambers receiving the liquid which passes out through the drum perforations and the other annular chamber receiving the solids which issue over the top edge of the drum.

A disadvantage of known sugar centrifuges of this kind is that the rotating drum sucks in external air and therefore produces a positive air pressure in the liquid receiving annular chamber. Some of this sucked-in air returns to atmosphere through liquid discharge piping which extends outside the centrifuge from the chamber, but some of the sucked-in air enters the solids-receiving annular chamber through an annular gap which exists between the top edge of the drum and the top of the annular partition. The air entering the solids-receiving chamber in this way carries drops of liquid along from the liquid chamber and these drops wet the centrifuged solid material which is now in the solids-receiving chamber, and this, of course, impairs the separation.

To obviate this disadvantage, centrifuges of this kind have been provided with an inner continuous casing which extends around the perforated screening surface of the drum and widens conically towards the top edge of the drum, the open top of the inner casing extending to near an outer continuous casing ring which is fixed to the top edge of the drum and widens downwards.

Consequently, when the drum rotates a flow of liquid and air is produced on the inside of the outer continuous casing ring and is intended to exert a suction on the annular gap between this casing and the partition separating the two annular collecting chambers from one another, the idea being to produce in the annular gap a flow of air directed into the liquid-receiving chamberi.e., to provide, as it were, a pneumatic sealing of the gap. Unfortunately, it is found in practice that this step alone cannot satisfactorily seal the annular gap and thus obviate any rewetting of the centrifuged solid material in the solids-receiving chamber.

It is an object of this invention so to improve a centrifuge of the kind described further to preclude flows of air through the perforated drum especially to the annular gap between the liquid-receiving chamber and the solids-receiving chamber.

To this end, according to this invention, a damming ring is provided on the inside of the outer continuous casing ring of the centrifuging drum and extends around the open top of the inner continuous casing.

The damming ring dams up the centrifuged liquid flowing from the inner continuous casing at the transition to the outer continuous casing ring so that a damming chamber which is formed here is filled with liquid and the top edge of the inner casing dips into this liquid. The gap between the centrifuging drum and the liquid-receiving annular chamber is therefore sealed hydraulically. Liquid which has been centrifuged through the perforated centrifuging viscous sugar compositions.

surface of the screening drum and which is rising along the inner continuous casing can readily pass by the damming ring, but no air can pass by the damming ring, for the specific weight of air is so low that the static pressure of the air is lower than the static pressure of the liquid in the damming chamber. Inhibiting the air flow in this region therefore ensures that no external air penetrates through the layer of centrifuged solid material on the drum and its screening surface and that there is therefore no extra cooling of the viscous material being centrifuged, cooling leading to a corresponding increase in the power required for the centrifuge. The action of the hydraulic seal in this respecti.e., reducing unwanted air circulation in respect of its cooling etfectcan be such as to make it unnecessary for the centrifuging drum to be specially heated externally or by the liquid chamber. Since the fan effect of the centrifuging drum is obviated, the power consumption of centrifuges according to the invention decreases once the damming chamber has filled up with liquid. The power saving, for instance, for centrifuges whose drum is 1200 mm. in diameter and runs at a speed of 1800 rpm, can be about 4.5 kw., or approximately 5%.

To reduce the risk of fine particles which have been passed through the drum perforations caking in the damming chamber, the damming ring is preferably spaced with spacer pieces from the face of the outer casing ring so that a narrow gap for the passage of solid particles present in the centrifuged liquid is left between the outer casing ring and the damming ring. In order to divide the liquid into solids-free liquid and solids-carrying liquid, at second annular partition is preferably disposed below the annular gap between the damming ring and the outer continuous casing ring and together with the first partition for the solids-receiving annular chamber bounds an intermediate annular chamber for collecting the solidscarrying liquid passing through the annular gap.

Advantageously, the spacer pieces are triangular and are placed between the outer casing ring and the damming ring with the vertex of each spacer pointing towards the damming chamber which is formed between the damming ring, the outer continuous casing ring and the top of the drumi.e., pointing in the opposite direction to the flow direction. The thickness of the spacers and the intervals between them determine the effective size of the interrupted annular gap between the damming ring and the outer continuous casing ring. The effective opening of the ring gap is so devised that the largest solid particles which have passed through the orifices in the centrifuging drum can pass through the annular gap, but the amount of liquid which can flow away is only such as ensures that the liquid in the damming chamber is always in contact with the inner continuous casing-i.e., the hydraulic seal cannot be made inoperative by an excessive outflow through the annular gap.

Another way of reducing caking of solids in the damming chamber and of separating the centrifuges liquid into solids-free liquid and solids-carrying liquid is for the outer continuous casing and/or the damming ring to be formed with appropriate passages which must be in the region of the dammed liquid.

An example of a centrifuge in accordance with the intop edge of the centrifuging drum; and,

FIGURE 3 is a view in developed form of a part of the damming ring and its spacers.

The centrifuge shown in the drawings is intended for The centrifuge comprises a screening and centrifuging drum 3 mounted in a casing 1 having a cover 2. The drum is rotatable about a vertical axis, widens conically upwards and is mounted in a bearing 5 screwed to a base 4 of the casing 1. The drum 3 is driven by a shaft 6 which extends vertically through the bearing 5 and is driven through a pulley 7 and V-belting 8 by an electric motor (not shown). The drum 3 has at its bottom end an upwardly widening imperforate accelerator pot 9. The sugar composition for centrifuging is supplied through a feed pipe 10 and is fed to the base of the pot 9 as a thickly viscous stream 11.

As shown in FIGURE 2, the drum 3 comprises a number of support bars 12 which extend in the direction of the drum generatrices and are inter-connected by a number of horizontal support rings 13 disposed at intervals one above another. A screen 14 in the form of a metal sheet formed with very fine screen perforations, is disposed on the inside edges of the rings 13. Extending around the outside of the drum 3 is an inner conical continuous casing 15 the open top 16 of which extends to near an outer downwardly widening conical continuous casing 18 disposed on the top edge of the drum.

A damming ring 20 is secured to the bottom end of the outer casing 18 by triangular spacers 19 disposed as shown in FIGURE 3. The thickness of the spacers 19 and the intervals between these spacers determine the effective size of the interrupted annular gap between the ring 29 and the casing 18. The vertices 19 of the spacers 19 point towards a damming chamber 21 which is bounded by the casing 18, by a ring 17 and by the ring 20. The top 16 of the inner casing 15 extends into the chamber 21. Liquid flowing along the bottom edge of the damming ring 20 in the direction indicated by an arrow 35 enters a liquid-receiving annular chamber 26 which has a cylindrical wall 24 having a cover 25 sloping downwards towards the outside. The wall 24 separates the chamber 26 from a liquid-receiving chamber 23 for receiving solids-conveying liquid which has passed along the damming ring 20 in the direction indicated by an arrow 22, through the discontinuous gap left by the spacers 19.

The liquid which has entered the chamber 23 leaves the centrifuge through a pipe 27 (see FIGURE 1) and the liquid which has entered the chamber 26 leaves the centrifuge through a pipe 28. A cylindrical partition 29 carrying annular plates 30 and 31 separates the chamber 23 from a sugar chamber 32.

The chambers 23 and 26 communicate through an annular gap 33 (see FIGURE 2) with the atmosphere. The casing 18 applies to the gap 33 a suction which would produce an air flow from the chamber 32 to the liquid- =receiving chambers 23 and 26 were it not for a covering ring 34 which simultaneously produces an oppositely directed suction. To this end, the casing 18 and ring 34 are of an outer diameter such that the oppositely directed suction effects are equali.e., cancel one another out.

Another way of obviating air flow between, the pipes 27 and 28, and the gap 33 is to provide an airtight closure of the outgoing pipes 27, and 28. To this end, the pipes 27 and 28 can dip below the level of liquid in tanks which are disposed after the centrifuge, or else the pipes 27 and 28 can have a siphon seal.

What I claim is:

1. A centrifuge for continuously separating mixtures of solids and liquids comprising a perforated centrifuging and screening drum which rotates about a vertical axis, two annular chambers disposed concentrically around the drum and separated from one another by an annular partition extending to the top edge of the drum, one of the annular chambers receiving the liquid which passes out through the drum perforations and the other annular chamber receiving the solids which issue over the top edge of the drum, an inner continuous casing extending around the perforated screening surfaces of the drum and Widening conically towards the top edge of the drum, the open top of the inner casing extending to near an outer continuous casing ring fixed to the top edge of the drum and widening conically downwards, a damming ring provided on the inside of the outer continuous casing ring and extending around the open top of the inner continuous casing, the damming ring damming up liquid to form a hydraulic seal between the inner casing and the outer casing ring.

.2. A centrifuge according to claim 1, in which the damming ring is spaced from the face of the outer casing ring so that a narrow gap for the passage of solid particles present in the centrifuged liquid is left between the outer casing ring and the damming ring.

3. A centrifuge according to claim 2, in which the narrow gap is formed by triangular spacer pieces disposed between the damming ring and the outer continuous casing ring, one vertex of each spacer pointing towards a d-amming chamber which is formed between the damming ring, the outer continuous casing ring and the top edge of the drum.

4. A centrifuge according to claim 3, in which a second annular partition is disposed below the narrow gap and together with the first mentioned partition bounds an intermediate annular chamber for collecting the solidscarrying liquid passing through the narrow gap.

5. A centrifuge according to claim 4, in which a cover ring is provided around the top edge of the drum, this ring having substantially the same outer diameter as the outer continuous ring and causing a suction to be applied to an annular gap around the top edge of the drum, the suction being oppositely directed and substantially equal to the suction applied to the annular gap by the outer continuous casing ring.

6. A centrifuge according to claim 4, in which liquid discharge pipes from the annular liquid chamber and the annular intermediate chamber are closed in an airtight manner.

7. A centrifuge according to claim 1 in which, in order to remove accumulated solids from the dammed up liquid, one of the outer continuous casing ring and the damming ring is provided with passages.

No references cited.

REUBEN FRIEDMAN, Primary Examiner.

I. DECESARE, Assistant Examiner. 

1. A CENTRIFUGE FOR CONTINUOUSLY SEPARATING MIXTURES OF SOLIDS AND LIQUIDS COMPRISING A PERFORATED CENTRIFUGING AND SCREENING DRUM WHICH ROTATES ABOUT A VERTICAL AXIS, TWO ANNULAR CHAMBERS DISPOSED CONCENTRICALLY AROUND THE DRUM AND SEPARATED FROM ONE ANOTHER BY AN ANNULAR PARTITION EXTENDING TO THE TOP EDGE OF THE DRUM, ONE OF THE ANNULAR CHAMBERS RECEIVING THE LIQUID WHICH PASSES OUT THROUGH THE DRUM PERFORATIONS AND THE OTHER ANNULAR CHAMBER RECEIVING THE SOLIDS WHICH ISSUE OVER THE TOP EDGE OF THE DRUM, AN INNER CONTINOUS CASING EXTENDING AROUND THE PERFORATED SCREENING SURFACES OF THE DRUM AND WIDENING CONICALLY TOWARDS THE TOP EDGE OF THE DRUM, THE OPEN TOP OF THE INNER CASING EXTENDING TO NEAR AN OUTER CONTINUOUS CASING RING FIXED TO THE TOP EDGE OF THE DRUM AND WIDENING CONICALLY DOWNWARDS, A DAMMING RING PROVIDED ON THE INSIDE OF THE OUTER CONTINUOUS CASING RING AND EXTENDING AROUND THE OPEN TOP OF THE INNER CONTINUOUS CASING, THE DAMMING RING DAMMING UP LIQUID TO FORM A HYDRAULIC SEAL BETWEEN THE INNER CASING AND THE OUTER CASING RING. 